People get confused by the tight constraints.

Based on P5's experience

Fixes https://github.com/flutter/flutter/issues/6628

Closes https://github.com/flutter/flutter/issues/5781

Closes https://github.com/flutter/flutter/issues/6125

On Android and Fuchsia, default to Roboto. On iOS, use San Francisco.

FormField is now a widget that can contain any type of field. Input no
longer has special code to handle form fields. Instead, there is a
helper widget InputFormField for using an Input inside a FormField.

Fixes https://github.com/flutter/flutter/issues/6097 and based on
feedback from the same.

TBR @abarth

...until people understand them.

Also eliminate unused accentColor-related properties.

Use the typography specified in the theme rather than Typography.white.

Fixes #6591

The theme fallback mechanism was busted by the shadowThemeOnly change.

Fixes #6562

* Use dark theme in GridTileBar

Reduce IconTheme, Typography hardcoding by applying a dark theme to the
contents. This is still not ideal; the theme brightness should really be
driven by backgroundColor.

* Add back IconTheme

Since IconTheme.of() finds the closest IconTheme, not the closest
IconTheme or Theme (which specifies IconThemeData), the previous commit
doesn't necessarily override any IconThemes futher up the tree.

Eliminates hardcoding of Typography.white in favour of picking up the
platform default typography from ThemeData.

Fixes https://github.com/flutter/flutter/issues/6451

Mostly around pointing people towards Block more aggressively.

Cancel button behavior for showdatepicker/showtimepicker

Fixes #6483 

Add some docs to explain how to use setState() wiht Checkbox, Radio,
Slider, and Switch.

Based on experience of usability study participant P1.

Based on observations of usability study participant P1.

This partially reverts https://github.com/flutter/flutter/issues/626 ,
but horizontal padding is not in the spec, so we still match the spec.

This patch removes uses of keyboard.mojom in favor of the
TextInputPlugin.

They support multiline text now.